Considerations on Switching Capability of Circuit Breakers under Earth Fault in Electrical Grid

Circuit-breakers are essential for the safety and reliability of electrical power systems by interrupting fault currents un-der various conditions. Circuit-breakers must be capable of breaking single-phase short-circuit currents which can occur in two distinct scenarios. The first scenario involves effective-ly earthed neutral systems, where single-phase faults can generate high fault currents that the circuit-breaker must safely interrupt to prevent equipment damage and ensure personnel safety. The second scenario occurs in non-effectively earthed neutral systems, where double earth faults can appear on two separate phases, with one fault occurring on one side of the circuit-breaker and the other on the opposite side. Such conditions pose significant challenges for circuit-breaker design and operation, requiring careful consideration of their dynamic response and fault current interruption capacity. This paper presents the expected be-havior of the circuit breakers and the real-life situations encountered during high-power testing of this type of equipment. Real-life testing reveals critical insights into per-formance limitations, transient phenomena, and operational reliability, providing valuable information for both equip-ment manufacturers and system designers. The study high-lights the importance of accurate modeling, thorough test-ing, and adherence to standards to ensure that circuit-breakers perform reliably under all anticipated fault condi-tions. The most severe condition is identified as a double earth fault occurring under phase opposition. Although additional tests are planned to confirm this, preliminary assessment suggests that under normal operating conditions (0° φ 30°), the current at the final breaking pole should not exceed the generator’s short-circuit current.